Noritz EZ Series & NCC199CDV Code 90
Combustion fault, unit shuts off. The same checklist as code 10, but the unit has stopped rather than just recorded it: air supply vent and exhaust vent for blockage, gas supply pressure checked by a professional, the condensate drain line clogged or frozen, the drain pipe sloping down, and the dip switch settings. Noritz adds that if the display continues after a power cycle, contact the nearest Noritz agent.
Also displayed as: F90
Call a proThe verdict
Call a licensed plumber
Two causes are free to check and genuinely common: the vent terminal outside and the condensate line. Everything past them is combustion, and a unit reporting abnormal combustion indoors is one to leave off rather than keep restarting.
Typical cost: $0–$1,000
US estimate for parts and labor. Prices vary by region and by who does the work — see how we estimate costs.
What the manual says
The meaning above is transcribed from the manufacturer's diagnostic documentation for the EZ Series & NCC199CDV — not averaged across the brand.
Source: Noritz Service Manual — NRC663 FSV, EZ98DV, EZ111DV, NCC199CDV (Rev. Oct 2017) (p. 32), read Sep 2026 — the manufacturer's own documentation for this exact series.
What you can safely check
Before anything else: if you smell gas, stop here, leave, and call your gas utility.
- Check the vent terminal and air inlet outside for snow, leaves, a nest or anything built against them.
- Follow the condensate drain line and check it is clear, unfrozen, and sloping downhill.
- Do not take any vent section apart yourself.
- If both are clear, or the code persists after one power cycle, call a licensed professional.
Frequently asked questions
Why is a blocked condensate drain a combustion fault?
Because on a condensing appliance the condensate leaves through the same system the exhaust does. When the drain backs up, water sits where flue gas needs to pass, and the unit sees the result as an air flow and combustion problem. It is why Noritz puts the drain line and the vent on the same checklist.
Code 90 on other Noritz series
The same code number can mean something different on another series — make sure you're reading the page for your exact unit: